docs: def make_signature(params, hmac_key):
      """
      Calculate a HMAC-SHA-1 (using hmac_key) of all the params except "h=".
  
      Returns base64 encoded signature as string.
      """
      # produce a list of "key=value" for all entries in params except `h'
      pairs = [x + "=" + ''.join(params[x]) for x in sorted(params.keys()) if x != "h"]
      sha = hmac.new(hmac_key, '&'.join(pairs), hashlib.sha1)
      return base64.b64encode(sha.digest())